Compositions that produce a color change upon exposure to energy in the form of light are of great interest in producing images on a variety of substrates. For example, labeling of optical storage media such as Compact Discs, Digital Video Discs or Blue Laser Discs (CD, DVD, or Blue Laser Disc) can be routinely accomplished through screen-printing methods. While this method can provide a wide variety of label content, it tends to be cost ineffective for run lengths less than 300-400 discs because the fixed cost of unique materials and set-up are shared by all the discs in each run. In screen-printing, a stencil of the image is prepared, placed in contact with the disc and then ink is spread by squeegee across the stencil surface. Where there are openings in the stencil the ink passes through to the surface of the disc, thus producing the image. Preparation of the stencil can be an elaborate, time-consuming and expensive process.
In recent years, significant increases in use of CD/DVD discs as a data distribution vehicle have increased the need to provide customized label content to reflect the data content of the disc. For these applications, the screen-label printing presents a dilemma as discs are designed to permit customized user information to be recorded in standardized CD, DVD, or Blue Laser Disc formats. Today, for labeling small quantities of discs, popular methods include hand labeling with a permanent marker pen, using an inkjet printer to print an adhesive paper label, and printing directly with a pen on the disc media which has a coating that has the ability to absorb inks. The hand printing methods do not provide high quality and aligning a separately printed label by hand is inexact and difficult.
It may therefore be desirable to design an optical data recording medium (e.g., CD, DVD, or Blue Laser Disc) which can be individually labeled by the user easily and inexpensively relative to screen-printing while giving a high quality label solution. It may also be desirable to design an optical data recording medium that accepts labeling via multiple methods, thus reducing the amount of inventory necessarily carried by optical data recording merchants and end users.
A variety of leuco dye-containing compositions have been investigated for use on optical disks and other substrates. Leuco dye compositions include a leuco dye along with an optional activator and an infrared absorber. However, many of these compositions are insufficiently stable when exposed to visible light. Many commonly used NIR radiation absorbers are cyanine dyes that have very good extinction in NIR range combined with very poor stability when exposed to visible light (especially blue part of the spectrum). Thus Leuco-dye compositions with cyanine radiation absorbers tend to have very good marking sensitivity in the beginning that decays at a fast rate when the coating composition is exposed to the visible light.